A nursery grows in the Great South Bay — and the young have several rows of teeth!

Fifteen juvenile sand tiger sharks have been tagged and tracked there in the past four years, making the bay a nursery ground for a protected species whose numbers have fallen worldwide, according to the Brooklyn-based New York Aquarium, which is heading the research. Ten were caught this year, and the five tagged in previous seasons have returned to the same section of the bay, a behavior known as “site fidelity,” scientists said.

The feeding and growing ground is exciting for Long Island’s marine biologists because the species has been overfished and hurt by being caught up in trawls and nets. Their presence in the nursery means they’re finding food in the bay, such as bluefish and bass, and protection against predators, including other sharks and people, experts said.

“If they’re doing well, then you know the whole system is doing well,” said marine biologist Joe Yaiullo, who founded the Long Island Aquarium in Riverhead, which has four sand tiger sharks. “It provides even more emphasis to protect those areas.”

The sand tiger shark is common in waters off Long Island but there are not a lot of them, he said. They are light brown, sometimes with darker red or brown spots, and reach lengths up to more than 10 feet. Yaiullo said boaters and fishers often mistake them for the more common sand shark and smooth dogfish shark.

No one knows how many sand tiger sharks feed or roam off Long Island, but the New York Aquarium’s research was considered a turning point in quantifying the state of health for this species. According to researchers there, only a handful of sand tiger shark nurseries have been identified, including one off Massachusetts.

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The New York Aquarium began tracking sand tiger sharks in the bay in 2011 after one of its scientists got a photo of a dead juvenile sand tiger shark from a marina along the bay. Scientists then started the tagging study using acoustic transmitters in Great South Bay. The sand tiger sharks they caught and then released were several months old to 5 years old, aquarium officials said.

“Sand tiger shark pups are not born here but migrate from down south to spend the summers as juveniles in New York’s coastal waters,” Merry Camhi, director of local marine conservation for the Wildlife Conservation Society, which runs the New York Aquarium, said in a news release. “The acoustically tagged animals in our study will help us better understand where the sharks go, their habitat needs, and how we can better protect them.”

Aquarium officials say there are many questions about the nursery. They don’t know how much of the bay is being used by sand tiger sharks. They want to find out how many juveniles spend their summers there and more about what they eat.

The sand tiger shark is considered a “species of concern” by the National Marine Fisheries Service and “critically endangered” in other parts of the world. They have been overfished as food and for their fins. Mating occurs every other year, with one or two pups in an average litter, the federal agency said, and sharks grow slowly. As a further hit to their numbers, sand tigers are inadvertently caught in fishing trawls, gillnets and longlines, the service said.